1. Field of the Invention
The present invention relates to a reading apparatus for reading a pattern formed on a sheet, and a printing apparatus including the reading apparatus.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2010-133915 discuses an ink jet printer including a colorimetric apparatus. This colorimetric apparatus performs colorimetry of a printed color pattern for color calibration and, based on colorimetric data, adjusts colors of a color image to be subsequently printed, thus reproducing desired colors. The printer records color patches as a color pattern for color calibration, and then the colorimetric apparatus performs colorimetry of the color patches with a colorimetric sensor moving in the sheet width direction.
When a carriage moves for reading, it is desirable to keep constant the distance between the sensor unit and the sheet and the posture of the sensor unit with respect to the sheet. With the printing apparatus discussed in Japanese Patent Application Laid-Open No. 2010-133915, the sensor unit is connected with the carriage by a connection mechanism, which allows the sensor unit to minutely rotate.
The connection mechanism for connecting the carriage and the sensor unit discussed in Japanese Patent Application Laid-Open No. 2010-133915 is a parallel link mechanism composed of two link plates on each side, a total of four link plates. Basically, the parallel link mechanism vertically moves the sensor unit with respect to the carriage. With the connection mechanism discussed in Japanese Patent Application Laid-Open No. 2010-133915, a plurality of shafts of the parallel link mechanism is loosely engaged with respective holes in an intentional way to provide “backlash”. This configuration enables the sensor unit to rotate within a minute range allowed by backlash, with respect to the carriage centering on two axes in parallel with the sheet.
With the connection based on such a loose parallel link mechanism, however, when the carriage moves, the sensor unit connected with the carriage shakes, thus degrading the positional accuracy of a colorimeter holder. In addition, when the carriage moves in an acceleration or deceleration motion, each link plate of the parallel link mechanism receives force to bend. Therefore, the positional accuracy of the sensor unit is also degraded by the bending of the link plates. If the positional accuracy of the sensor unit degrades, a small-sized color pattern cannot be read.
This means that, with the printing apparatus configuration discussed in Japanese Patent Application Laid-Open No. 2010-133915, it is required to increase the size of color patches to be formed on the sheet. Therefore, the sheet consumption required for color calibration increases, and the amount of sheet conveyance in color calibration increases, thus resulting in an increase in time period required for color calibration.